Grinding machine



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R. w. YOUNG 1,965,020 GRINDING MACHINE v11661 Nov. l5. 1930 '7Sheets-Sheet l @OM HMM July 3, 1934.

R'. W. YOUNG GRINDING- MACHINE Filed Nov. 15, 1930 7 Sheets-Sheet 2 R.W. YOUNG GRINDING MACHINE l Filed Nov.`15. 1930 '7 Sheets-Sheet 3 My 33934 R W. YQUNG 1,965,020

GRINDING MACHINE vFiled Nov. l5, 3.930 7 Sheets-Sheet 4 Juy 3, E934 R.W. YQUNG l965,020 Y GRINDING MACHINE Filed NOV. 15 1930 7 sheets-sheet 6l Jaw/2%# @OWMUMM MQ' Judy 3 i934.

R. W. YQUNG LGSZG GRINDING MACHINE Filed Nov. l5, 1930 7 Sheets-Sheet 7@//MJ www,

Patented July 3, 1934 UNITED STATES istanza PATEN QFFCE GRINDING MA EINEcorporation cf Illinois Application November 15, 193i), Serial No.495,825

6 Claims.

This invention relates to improvements in grinding machines and moreparticularly to a type of automatic multiple spindle grinder designed tomeet the demand for increased production without sacrificing accuracy inthe dimensions of the finished Work.

Accordingly the object of the invention is to provide a grinding machinewhich will operate continuously without the necessity of periodicadjustments to compensate for wear of the abrasive elements, this beingaccomplished by continuously feeding the grinding wheels toward the workat the rate calculated on the normal Wear on the grinding face, andsimultaneously dressing the faces of the wheels so that they not onlypresent the most efficient cutting surface to the work at all times, butare continually maintained in planes xed as the dimensional limits forthe ,work passing therebetween.

A further object of the invention is to provide a grinding machinehaving two or more sets or pairs of grinding wheels whereby the work isadvanced from one set to another, thus undergoing a succession ofgrinding operations, as for instance, the roughing, semi-iinishing andiinishing operations. These sets of grinding wheels are moreoverindependently driven and adjustable so that the amount of metal removedby each may be varied to meet different working conditions.

Before undertaking the description of the machine embodying the featureshereinbefore enumerated, it may be observed as a matter of generalknowledge that heretofore machines have been designed for work of thischaracter which include a pair of spaced grinding wheels 'between whichthe work is advanced. Manifestly, the spacing of the Wheels determinesthe nal dimension of each piece, and so long as the spacing does notvary, the work will be uniform. But grinding wheels are subject to wear,and hence require periodic readjustments when the 'allowable error indimension has been reached. Furthermore, the surface of a grinding wheelbecomes dull after a period of use, due to the fact that the abrasiveparticles become worn to such an extent that their cutting action isimpaired, from which it follows that the work offers greater resistanceto the grinding wheels, thus subjecting the machine to greater strainsand demanding more power to drive it. This condition also must beremedied by periodic dressing of the wheel surfaces, so that in theordinary type of grinding machine the operation is continually beinginterrupted for readjustments, which not only reduces the output but theaccuracy of the work, which is wholly dependent upon the care exercisedby the operator in resetting the wheels. And iinally betweenreadjustments there is a continuous change in the operating conditionsas well as the character of the work being performed, G0 inasmuch as thewearing and dulling of the wheels is a gradual process.

By visualizing a pair of grinding wheels which are constantly movingbodily toward each other at a scarcely perceptable rate of speed, andeach wheel provided with an accurately set diamond point dressing toolwhich passes across the face of the wheel, say, once in every 250revolutions, it is possible to gain a general idea of the principleunderlying the construction and operation of the improved machine.

As an example of the class of Work for which the improved machine may beused to advantage, the present disclosure shows a type designed for thegrinding of valve tappets used in the manulacture of internal combustionmotors, the particular operation being that of removing a given amountof metal from each end in three stages so that they are iinished to anexact length. Such a machine is illustrated in the accompanyingdrawings, wherein Figure 1 is a view in front elevation of the machinewith parts broken away to show parts concealed within the casing.

Figure 2 is a view in end elevation of the 85 machine.

Figure 3 is a view in vertical section taken transversely through themachine on line 3-3 of Figure l.

Figure 4 is an enlarged detail View of a section 90 of the feed drum.

Figure 5 is a view in vertical section taken longitudinally through themachine on line 5-5 of Figure 2.

Figure 6 is a vertical section through one end 95 of the machine astaken on line 6-6 of Figure 5.

Figure 7 is an enlarged detail view or" the driving gear for theoscillating wheel dressing mechanism as taken on line '7-7 of Figure 5.

Figure 8 is an enlarged detail in elevation of 100 one of the diamondpoint setting devices.

Figure 9 is an enlarged detail View in vertical section through thedriving end of the machine, as taken on line 9-9 of Figure 2 and showingthe drive for advancing the grinding wheel units.

Figure 10 is an enlarged detail View of one of the release locks for thefeed shaft of one of the grinder units, taken on line 10-10 of Figure 9.

Figure 11 is a sectional View of the feed drum as taken on line ll-ll ofFigure 4, showing the 11,0

Loeaoeo wheel 12 and which meshes with another gear wheel 21 immediatelybelow it. On the same shaft with the gear wheel 21 and turning with itis a worm 22 (Figure 2), which in turn meshes with two worm wheels 23and 24, the former being mounted on a vertical counter-shaft 25 midwayof its ends, and the latter mounted on one end of a horizontalcounter-shaft 26 extending toward the rear of the machine housing. Now,the vertical shaft 25 is offset from the ends of the lead screws 19, 19of the upper and lower grinding units, and the ends thereof arejournalled in bearing brackets 27, 27 (Figure 9) which also serve asbearings for extremities of the lead screws exterior the end of themachine housing.

Mounted at the lower and upper ends of the counter-shaft 25 are worms28, 29 which mesh with worm wheels 30, 31 on the lower and upper leadscrews 19, 19, respectively. Similarly the horizontal shaft 26 carriesat its rear end a worm 32 which meshes with a worm wheel 33 on the endof the screw shaft 19 of the rearmost or intermediate grinder unit(Figure 2).

Now, both shafts 25 and 25 are driven at the same speed from the shaft 5of the feed drum, but a slightly variable speed is imparted to the leadscrews by using worms and worm wheels of different pitch, that is, thelead screw for the roughing grinder unit is driven from the countershaft25 with a single pitch worm and worm wheel, the semi-finishing unit witha double pitch worm and worm wheel, and the finishing unit with a triplepitch worm and wheel, so that there is a corresponding reduction in thespeeds of the three lead screws.

Thus, the lead screws to the roughing grinding wheel units may turn atthe rate of, say, 1 revolution in 100 minutes; the semi-finishing unitlead screws at 1 revolution in 30() minutes, and the finishing unitshafts at 1 revolution in 400 minutes. These speeds, however, are notdefinite but `merely indicative of the slow speed at which the screwshafts turn and the relative speeds between them. Manifestly thesespeeds are further reduced in the conversion of the rotative movement ofthe lead screws to linear motion of the grinder units through theintermediate 'threaded connection, so that the actual movenient ofwheels is, say, from to 1/8 of an inch in 3 hours of continuousoperation, or equal to the rate at which the wheels wear during the sameperiod plus the amount removed by the dressing operation.

Referring further to one of the grinding units,

^ it is to be observed that when the grinding wheel has been worn tosuch a degree as to require renewing, or in initially setting the wheelat the commencement of a grinding operation, it is necessary to providefor the shifting of the unit by hand. Hence provision is made fordisconnecting the lead screw from its driving countershaft and turningthe same by a crank. Thus in Figure 10, the lead screw 19 may be one ofany of the six grinding units', say, the lower unit shown in Figure 9,and is driven from the vertical counter-shaft 25 by the worm 28 and wormwheel 30. It will be noted that the end of the lead screw 19 extendsbeyond the wheel 30 in a square end 19a and just inwardly therefrom is athreaded portion 19h on which is a nut 34, which bears against a clutchcollar 35 slidably keyed to the screw shaft and coacting with acomplementary clutch member a in the form of clutch teeth formed at theend of the hub portion of the worm wheel 30, which mesh with teeth a onthe adjacent face of the clutch collar 35. Between the clutch collar 35and the worm wheel 30 is a clutch spring 36 so that by backing off thenut 34 the clutch teeth are disengaged, thus permitting the worm wheelto turn loosely on the screw shaft and permitting the latter to beturned by applying a crank 37 to the square end.

As heretofore explained, the dressing of the grinding wheels isperformed by pointed diamonds which travel across the cutting face ofeach wheel at prescribed intervals. Each wheel has its separate dressingappliance, and the same general arrangement is used throughout.

Referring particularly to Figures 5 to 8, and to one of the dressingdevices, the pointed diamond 38 is set into a metal holder 39 which inturn is mounted at the end of a rocking lever 40 carried at the end of arock shaft il and journalled in a bearing 42 supported in one of the twovertical walls la, la which enclose the space in which the grindingwheels are located as shown in Figure 5. Manifestly there are sixdressing devices, one to each wheel, and each is independent of theothers, although each group of three on opposite sides of the feed drumare driven from a single source of power as will presently be described.

Now, the axis of each rock shaft is offset out- '-1 wardly beyond theperiphery of its associated grinding wheel, as well as the path of thework, so that the rocker arm holding the diamond swings back and forthin a plane parallel with the face of the wheel with the diamond pointprojecting toward the same.

As shown in the drawings, Figure 6, the grinding Wheels are of the ringtype and not solid discs so that the diamond point need only travelthrough a relatively small arc in order to traverse the face of thewheel.

Now, the point of the diamond, or better7 the plane transversed therebydetermines the plane of the cutting surface of the wheel, and henceprovision must be made for setting the diamond point. Beyond the arc oftravel of each diamond pointed dressing tool, but in prolongationthereof, is a gauge plug 43 mounted in the vertical walls la of thehousing on the adjacent side of the feed drum. These plugs are pins ofhardened steel which are mounted in suitable bearings in said walls la,with end portions having flat faces projecting into the spaces onopposite sides of the feed drum. Each plug is adjustable endwise, have aknurled inner end portion 43a,

and a lock-nut 43h for securing the plug in position. There is a pair ofgauge plugs for each pair of grinding wheels which are located exactlyopposite each other so that the distance between them can be measuredaccurately, this 1e distance being the dimension to which the pieces areto be reduced by the particular pair of grindlng wheels with which thegauge plugs are associated. Thus if the points of the diamond dressersare set so they just touch the ends of the gauge plugs, it follows thatthe faces of the wheels will be dressed to coincide with the planesinitially established by the setting of the gauge plugs.

The setting of the diamond points manifestly is completed before thegrinding operation is commenced, and in so doing it is necessary totemporarily disconnect the rock levers holding the diamond points fromthe rock shaft so that they can be swung beyond their normal arc oftravel, as well as to be shifted endwise in order to bring the pointsinto contact with the ends of the plugs.

As a preferable arrangement, each rock shaft 41 is split near thebearing 42 at its forward end, and its adjacent ends inserted into asleeve 44 (Figure 8), having a radial arm 44a. The main section of therock shaft 4l is keyed to the sleeve as at 41a, while the other shortsection 41a. carrying the rock lever 40 fits loosely in the oppositeendy of the sleeve, and has a collar 45 fixed thereto which is providedwith a shouldered abutment face 45a normally intertting with acomplementary abutment face at the end of the sleeve 44. And finally alock ring 46 surrounds the collar 45 on the shaft and has threadedengagement with the end of the sleeve 44, so that when the lock ring istightened the collar is drawn up against the sleeve and the sections ofthe shaft are united. Now, projecting from the inner end wall la of thehousing is a rod 47 located below and offset to one side of the rockshaft but in line with the end of the radial arm 44a of the sleeve 44.At the end of this rod is attached a coil spring 48 which is secured tothe end of the radial arm 44a and extends at right angles thereto. Thusthe rocking movement of the shaft 41 and lever 4i) is resisted bythetension of the spring, it being manifest that the sleeve 44 rocks withthe shaft, since it normally joins the split ends together. However, onloosening the connections between the sections of the shaft, by backingoff the lock ring 46 from the threaded end of the sleeve 44, the section41a of the shaft 4l beyond the collar and the arm 40 holding the diamondare disconnected from the main section of the shaft 4l and are thus freeto be swung through the extended arc necessary to bring the diamondpoint opposite the end of the gauge plug 43 for its initial setting.

Assuming then that the diamond points are set from the gauge plugs andthe rocker arms 40 are lockedy to their rock shafts, the movement of thepoints across the face of the grinding wheels will remove a minute layerof abrasive over and above the normal wear in contact with the work.This is because the wheels are being constantly fed or advanced towardthe work, and simultaneously dressed, so that their surfaces are alwaystrue, and maintained at a high degree of cutting efficiency, and of moreimportance their surfaces are always coincident with the xed planesestablished by the gauge plugs.

In addition to the disengagement of the rocker arm holding the diamondpoints permitting their free swinging movement to the gauge plugs 43,provision must also be made for shifting the rocker arm laterally oraxially of their rock shafts in order to bring the points of thediamonds into contact with the faces of the plugs. This is accomplishedby a separate adjustment between the short section of the shaft 41a andthe hub-portion 40a of each diamond point holding rocker arm 40 (Fig.8). Without going into detail as to exact arrangement, which may bevaried to obtain the same results, the adjustment is in the nature of athreaded connection between the end of the short shaft section 41a and acollar 49 mounted on the inner end of the hub-portion 40a of the rockerarm 4f) and beyond the bearing 42, and having a micrometer scale 49aabout its periphery with a pointer 49h mounted on the bearing 42a.Suitable looking means (not shown) are employed so that by rotating thecollar 49 the rocker arm is shifted just enough in either direction toafford the necessary adjustment. The divisions on the micrometer are inthousandths of an inch and calculated to the pitch of the threadsconnecting the end of the shaft 41a andthe hub 40a of the rocker arm, sothat by turning the adjusting collar 49 so many divisions on the scalewill shift the point of the diamond a corresponding distance in an axialdirection.

It is to be observed, moreover, that while the diamond points are veryhard, they nevertheless undergo an appreciable wear, which must be takeninto account if accuracy is to be insured. It can be pretty wellestablished by test the rate at which a diamond point will wear down inuse, and compensation duly made therefor by the same micrometeradjustment. Thus, having determined the setting of the diamond point bythe pointer on the scale 49a at the beginning of the grinding operation,and knowing the rate at which the points wear down, the necessaryadjustment for wear can be made by the operator from time to timewithout interrupting the operation of the machine or resetting thepoints from the gauge plugs.

Referring now to the driving mechanism for the wheel dressing devices,each of the rock shafts 4l extends lengthwise of the housing on eitherside of the grinding wheels and are journalled` at their outer ends inbearings provided in the outer end walls lb (Figure 5).

The mechanism for imparting a rocking motion to these rock shafts willnow be described. Near the outer ends of the machine housing andsupported upon the base casting 2 is an electric motor 50, it beingobserved that the same mechanism is duplicated at the opposite end ofthe machine. This motor is directly connected with a variable speedreducer 51 of a standard design. The speed reducer in turn is directlyconnected to a train of gearing including a miter gear 52 mounted on thedriven shaft 51a of the speed reducer 51 (Figure '7) which in turnmeshes with a larger miter gear 53 mounted on a shaft 54 carrying a worm55, the latter meshing with a worm wheel 56.

The gearing just described is enclosed within a gear case 57, providedwith bearings for the several elements therein. On the shaft 56asupporting the worm wheel 56 is a crank plate 58 to which is journalleda short connecting rod 59 connected with a rocker arm 60 keyed to thelowermost rock shaft 4l, and extending upwardly in a vertical direction.Also mounted on the lower rock shaft 4l is another rocker arm 60aextending approximately at right angles to the rocker arm 60 and in arearwardly direction (Figure 6). A long link 61 connects the rocker arm60a with a parallel rocker arm 62 on the rock shaft 4l directly aboveand near the top of the machine housing. Also connected with the rockerarm 60 is a shorter link 63 extending horizontally and rearwardly and isconnected with a rocker arm 64 on the intermediate rock shaft 41. Thusall of the rock shafts 4l which operate the three diamond point dressersfor the corresponding groups of grinding wheels are fe driven from asingle power unit, there being a similar unit at the opposite end of themachine for the other group of dressers as heretofore explained. Thusduring the operation of the machine these diamond point dressers arecontinually oscillating across the faces of the grinding wheels, say,once in every five or six revolutions of the wheels, although the speedof oscillation can be varied, depending on the class of work beingperformed.

lwise therein alternately pets after y 1t remains' now to discuss thework feeding device, and in this connection it may be stated that adetailed description is unnecessary inasmuch as this part of the machineis an adaptation of an already well known construction.

Thus in Figure 1 are shown two hoppers 65, 65 into which the work to beground is piaced, which in this case are valve tappets T shown inFigures 11 and 12. These hoppers are located on 0pposite sides of thefeed drum 4 and at the iront of the machine, and are kept filled by theoperator. Leading from` the hoppers are guideways a, 66 (Figure 3)extending to the periphery of the feed drum. It may be explained thatthe tap-- pets are fed to the chute alternately from each hopper, and inso doing are presented to the feed drum with their head ends alternatelyreversed as shown in Figure 12.

As already explained, the feed drum 4 has the general form oi a disc andabout its periphery is a ring 67 made up of segments or blocks ofchannel section bolted to the disc. The ring thus formed has an annulargroove between radial flanges 67a, 67a extending entirely around thedisc, and through the flanges are drilled sets of registering holes orbores 67h sized to receive the shank portions of the tappets T. Eachblock or segment oi this ring 67 is provided with two of the holes 6719located near opposite ends, andl between the anges midway between eachpair ci holes is a toggle operated work retaining device consisting ofpivotaliy connected pressure fingers 68, 68 extending endwise toward theholes 67h (Figure 4), a spring pressed plunger 69 below the togglejoint, and a toggle lever 70 pivoted at a point oiset from and bearingon the pressure :lingers at the toggle joint. Each toggle lever 'l0extends somewhat tangentially to the periphery of the disc and in adirection opposite the direction of rotation of the disc which iscounterclockwise.

Thus as shown in Figure 3, the periphery of the disc carries a pluralityof the toggle levers To, each operating a set of work-retaining pressurenngers ior two pieces of work T. Surrounding the periphery of the discis an endless sprocket chain 7l which is led away from the disc adjacentthe point at which the work is fed thereto, and travels about a smallidler sprocket 'l2 mounted at the upper end of a vertically arrangedlever 73 pivoted intermediate its ends and provided with a tensionadjusting spring .'74 at its lower end for varying the tension of thesprocket chain. The chain travels in the plane oi the toggle levers 70,and as each comes into contact with the lower lead of the chain, it ispressed down, thus actuating the pressure fingers to hold the tappets Tin place within their bores, said tappets having been previouslyinserted endfrom opposite sides of the reed drum. Mechanism is providedfor feeding the tappets into the feed drum from the chute 66, andlikewise for discharging the finished tapthey have been carried aroundalmost a complete revolution on the disc and between the three sets ofgrinding wheels. This part of the feeding mechanism, however, has beenomitted for reasons already stated, and particularly since it issomewhat complicated although typical of automatic feeding devices.

1t will suffice to say, therefore, that each tappet is fed to the feeddrinn and locked in place before reaching the first set of grindingwheels 13, 13, and are released and discharged from 65d which connectwith an inclined chuteA the drum after passing between the last orfinishing grinders 15, 15.

As an example of the manner in which the grinding operations areperformed, it may be assunied that the tappets are 2.260 inches inlength in the rough, and are to be finished to 2.245 inches,

in other words, .015,inch of metal is to be removed. Now, this metal isto be removed from each endl and in three grinding operations, so thatthe three .Y sets of grinding wheels must be initially set to rey Thusthe move their predetermined portion. gauge plugs for rough grindingwheels 13, 13

would be set 2.250 inches apart, so that .010 inch would be removedduring the rst or roughing cut. Similarly the semi-finishing grinderswould,

be set to 2.245 inches to remove .004 inch, and finally the finishinggrinders are set at 2.245 indica-the specified length,so that they wouldremove only the remaining .001 inch of metal.

However, it is to be observed that the path of the work between the setsof grinding wheels is nearly diametrical, and since the grinding wheelsare ring shaped, each tappet transverses two cut-..

ting surfaces, that is, as it enters the space between two wheels and asit leaves. Now, it is deemed to be productive of greater eihciency todivide the work accomplished by each set of wheels in two operations orcuts, rather than remove the entire amount in a single cut, as forexample, as the tappet enters the grinding Zone. This division of thework can be readily accom-` plished by offsetting the axes of each setofl wheels just enough so that the surfaces will be slightly nearertogether at the rear or leaving side ci the grinding zone, than at theforward or entering side. This arrangement is shown greatly exaggeratedin Figure 12 in which the planes of l the wheels are shown as convergingslightly in the direction traversed by the work and a tappet enteringand leaving the grinding zone.

Thus if these wheels are assumed to be the rough grinders and the totalamount of metal to be removed is .010 inch, the axes of the wheels wouldbe offset so that at the entering edges they are spaced apart 2.255inches and 2.250 inches at the leaving edges. Thus .005 inch of metal orone-half the full amount would be removed during the entering cut andthe remaining .005 inch would be removed on the second or leaving cut.l

'125. ed `more uniiormly and the power required to drive them can bereduced accordingly, inasmuch as no- In this way the wear on the wheelsis distributone cutting surface takes the full depth of cut. Similarlythe other wheels would be set to divide the work between the enteringand leaving cuts. And finally the tappets are alternately reversed endto end in order to evenly distribute the wear between the grindingwheels of each pair, inasmuch as a greater amount is removed from thehead end.

1t will be understood that while the machine herein disclosed isespecially designed for the grinding of tappets, other shapes of workmay be operated upon in the same manner, as for instance, valves orother metal parts which are to be reduced to a given length or thicknessby grinding opposite end or parallel surfaces.

The advantage of such a machine for grinding operations is the greatlyincreased production that is obtainable and the accuracy of the workperformed, due in part to the fact that the inachine can operatecontinuously and for long periods of time without interruptions foradjustments or dressing of the wheels, and aga-in because the grindingsurfaces are always in a deiiics,

nite plane and maintained at the highest degree of cutting efliciency.

Having' set forth a preferred embodiment of my invention, I claim:

1. In a grinding machine, the combination of a rotative feed drum, inwhich the Work to be ground is advanced through a circular path, a pair'of rotative grinding Wheels mounted on opposite sides of said drum andin the path of the work, a pair of adjustable gauge plugs adjacent saidWheels adapted to be set to determine the cutting planes of said wheels,a pair of rocker arms journalld adjacent said Wheels and said gaugeplugs and carryirm diamond point dressers extending toward the faces ofsaid wheels, rock shafts `connected with said rocker arms, driving meansfor said rock shafts including separate motor driven speed=reducingunits operative to rock the same through a predetermined arc, and meansfor temporarily disconnecting said rocker arms from their shafts topermit the initial setting of said diamond point dressers in contactwith said gauge plugs. i Y

Y2-. In a grinding machine, the combination of a rotative feed drum, inwhich the work to be ground is advanced through a circularpath, a pairof rotative grinding wheels mounted on opposite sides of said drum andin the path of the Work, a pair of adjustable gauge plugs adjacent saidWheels adapted to be set to determine the cutting planes of said Wheels,a pair of rocker arms journalled intermediate said Wheels and said gaugeplugs and carrying diamond point dressers extending toward the face ofsaid wheels, driving means for said rocker arms including motor drivenspeed-'reducing units, means for temporarily disconnecting saidgrockerarms from said driven means to permit the initial setting of saiddiamond point dressers in contact with said gauge plugs, and means forfeeding said grinding Wheels bodily toward the planes defined by theoscillating points of said dressers.

3.` In a grinding machine, the combination of W'ork feeding means, apair of grinding Wheels mounted on opposite 'sides of said Work feedingmeans, a pair of adjustable gauge members adjacent said grinding wheels,and adapted to determine the plane of grinding of each Wheel, a dressingtool mounted adjacent each of said wheels and 'adjustable for settingfrom said gauge members, and mechanism for operating said dressers toperiodically dress the surfaces of said' wheels during the grindingoperation.

4. In a grinding machine, the combination of continuous Work feedingmechanism, a pair of grinding wheels mounted on opposite sides of thepath of the Work in said feeding mechanism, a gauge plug mountedadjacent each of said Wheels and adjustable endwise to determine theplane of grinding of each Wheel, a dressing tool associated with eachwheel and comprising an oscillating arm, driving mechanism for saiddressing tool including mechanism for imparting oscillatory movement tosaid arm, and means permitting the said arm to be disconnected fromA itsdriving mechanism for its initial setting in contact with its gaugeplug.

5. In a grinding machine, the combination of continuous Work feedingmechanism, a pair of grinding Wheels mounted on opposite sides of thepath of the Work in said feeding mechanism, a gauge plug mountedadjacent each of said Wheels and adjustable endvvise to determine theplane of grinding of each wheel, and a dressing tool asso ciated witheach grinding Wheel comprising a rocker arm, a motor, and mechanismintermediate said motor and said rocker arm for imparting anintermittent oscillating movement to the latter.

6. In a grinding machine, the combination of a pair of opposed motordriven grinding Wheels slidably supported for axial movement, means forcontinuously feeding the Work to be ground between said grinding Wheels,mechanism driven from said Work-feeding means for advancing saidgrinding vwheels at a constant and relatively slow speed toward the workduring the grinding operation, dressing tools mounted adjacent saidgrinding wheels and each comprising a rocker arm adapted to swing in anarc including cutting face of its respective grinding Wheel, said armsbeing adjustable axially of said grinding wheels, gauge plugs coactingwith said rocker arms for initially setting the points of said dressingtools to a predetermined distance between the cutting faces of saidWheels, and independent driving mechanism for each of said dressingtools including a motor and speed-reducing gearing for imparting anintermittent oscillating movement to said tool-holding arms.

RALPH WALDO YOUNG.

